Siphonaptera

Fleas

Ctenocephalides felis, the cat flea shown here, is a typical
member of the Siphonaptera ("sucking-wingless"), the fleas. Although known to
be related to the true flies (the Diptera) by details of internal structure,
the Siphonaptera are highly modified for a parasitic existence; they have
no wings and no compound eyes, the legs are modified for jumping,
the antennae are very short and recessed in grooves on the head,
and the body is highly flattened laterally. Most are parasites on
mammals; a few live on
birds.
Adult fleas feed on blood, while their larvae feed on organic debris.

Fleas are extremely rare as fossils; their small size and specialized habitat
makes them highly unlikely candidates for fossilization. Two species have been
found in amber from the Baltic region (late Eocene-Oligocene);
living members of the family of fleas to which these fossils belong
(Hystrichopsyllidae) are mostly
parasitic on insectivores (moles and shrews). A few Cretaceous fossils have been
assigned to the Siphonaptera (e.g. Riek, 1970), but some of these fossils are
questionable (Carpenter, 1992). Since the
Siphonaptera are mostly parasitic on mammals, they presumably evolved at
about the time the mammals were evolving, in the
Jurassic and Cretaceous.

Researchers, and those who just can't get enough information on fleas, shoulddefinitely check out
Flea News,
a biennial newsletter put out by the Department
of Entomology at Iowa State University.